Control apparatus for cylinder fuel injection internal combustion engines

ABSTRACT

PCT No. PCT/JP97/01441 Sec. 371 Date Apr. 28, 1998 Sec. 102(e) Date Apr. 28, 1998 PCT Filed Apr. 24, 1997 PCT Pub. No. WO98/09063 PCT Pub. Date Mar. 5, 1998A control apparatus for a cylinder fuel injection internal combustion engine in which a compression stroke injection mode for carrying out fuel injection mainly in a compression stroke and a suction stroke injection mode for carrying out fuel injection mainly in a suction stroke can be selected in accordance with the operational condition of the engine. The apparatus aiming at enabling a suitable suction correcting amount to be set for each operational mode of the engine and the improvement of drivability thereby being improved.

This application claims the benefit under 35 U.S.C. § 371 of prior PCTInternational Application No. PCT/JP97/01441, which has an Internationalfiling date of Apr. 24, 1997, which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreferences.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a control unit for in-cylinder injectioninternal combustion engine which can select, according to an engineoperation state, a compression stroke injection mode for mainlyinjecting fuel at a compression stroke and an intake stroke injectionmode for mainly injecting fuel at an intake stroke; and, in particular,to a control unit for in-cylinder injection internal combustion enginewhich can optimally correct an intake amount.

2. Background Art

A throttle valve is installed in an intake passage of an engine such asan internal combustion engine. There has been developed a configurationof an intake system in which a bypass passage bypassing thethrottle-valve-installed portion is formed such that its both endportions communicate with the intake passage, and the bypass passage isequipped with a bypass valve.

Commonly employed as such a bypass valve is, for example, a bypass valvefor idle speed control which is used for adjusting the intake amount sothat the engine can maintain a predetermined idling rotational speed.

Independently of a throttle valve whose opening degree is adjusted inresponse to a driver's operation for stepping on an accelerator pedal,the opening degree of the idle speed control bypass valve isappropriately adjusted, while feeding back the engine rotational speed,in order to keep the engine rotational speed at a predetermined idlerotational speed, and independently of the driver's accelerator pedaloperation, the intake amount is adjusted so as to maintain the idlerotational speed.

Also, there has been developed a configuration of an intake system inwhich, separately from the bypass passage for idle speed control and thebypass valve, a bypass passage for bypassing thethrottle-valve-installed portion of the intake passage is formed so asto be used for controlling the air/fuel ratio of the air/fuel mixturesupplied to a combustion chamber not only upon idling, and this bypasspassage is equipped with a bypass valve [which is referred to as airbypass valve (ABV)].

Such an air bypass valve can control not only idle speed but also otherengine operation states by adjusting the intake amount independently ofthe throttle valve that is adjusted upon the driver's accelerator pedaloperation.

In any case, the opening degree of these bypass valve is appropriatelycontrolled according to the engine operation state or the like,independently of the throttle valve that is adjusted by the driver'saccelerator pedal operation.

Also, when the idle speed is to be controlled by such a bypass valve, atarget engine rotational speed is set according to cooling watertemperature, air conditioner state, shift lever position (in the case ofautomatic transmission), or the like, and while an actual enginerotational speed is being detected, the opening degree of the bypassvalve is adjusted so that the actual engine rotational speed coincideswith the target engine rotational speed.

When the bypass valve is used for the purpose other than idle speedcontrol, by contrast, an air amount (intake correction amount) to betaken in by the bypass valve is set according to the engine operationstate, and the opening of the bypass valve is adjusted to such a degreethat this air amount is attained. In this case, a relationship betweenthe engine operation state and its corresponding intake correctionamount or valve opening degree may be mapped, for example, and theintake correction amount or valve opening degree is set while the engineoperation state is caused to correspond to this relationship (map).

Further, there is a technique in which a motor-driven throttle valve isprovided such that the throttle valve is driven by a motor, while atarget opening degree of the throttle valve is set on the basis ofvarious correction coefficients set according to the accelerator openingdegree and operation state, thus allowing intake adjustment to beeffected without using a bypass valve or the like.

Meanwhile, recently under development are lean-burn engines whichperform a burn operation in a fuel-lean air/fuel ratio state. Widelyused in such a lean-burn engine is a multi point injection (MPI) typeengine in which intake ports of individual cylinders are provided withrespective fuel injection valves, since it can control the fuelinjection amount in each cylinder and thus has a good controllability.In a recently-developed in-cylinder injection engine (in-cylinderinjection internal combustion engine) in which a fuel injection valve isdisposed so as to directly inject fuel into a combustion chamber withina cylinder, an ultra lean burn operation, in which a burn operation isperformed in a further fuel-lean air/fuel ratio state, can be effected.

Namely, since fuel can be injected into the combustion chamber in suchan in-cylinder injection engine at any time regardless of opening andclosing of the intake valve, various operations, including the ultralean burn operation, can be performed as explained in the following.

For example, a fuel injection mode based on a compression stroke(referred to as compression stroke injection mode) can be set. In thiscompression stroke injection mode, stable burning can be realized in anultra lean air/fuel ratio state due to stratified combustion utilizing astratified intake flow formed within the cylinder. Namely, since theinjected fuel can be concentrated in the vicinity of a spark plug; whileonly the vicinity of the spark plug attains a stable ignitionperformance as an air/fuel ratio state with good ignitability (i.e.,state at a stoichiometric air/fuel ratio or an air/fuel ratio in whichfuel is somewhat richer than that in the stoichiometric air/fuel ratio),an ultra-lean air/fuel ratio state is attained as a whole so as toenable driving while greatly saving fuel consumption.

Of course, a fuel injection mode based on an intake stroke (referred toas intake stroke fuel injection mode) can be set. In this intake strokefuel injection mode, while the air/fuel ratio state of the wholecombustion chamber is being homogenized by premixing the fuel, operationcan be performed so as to realize stable ignition and secure flamepropagation, thereby attaining a sufficiently high output. Adopted asthis intake stroke injection mode are a stoichiometric mode forattaining a higher output while adjusting the air/fuel ratio to thevicinity of a stoichiometric air/fuel ratio and a lean mode for settingthe air/fuel ratio leaner than the stoichiometric air/fuel ratio wherebythe fuel consumption can be saved. Also, in view of the case where ahigh output is temporarily required upon sudden acceleration or thelike, adopted is an enriched mode in which the air/fuel ratio is madericher than the stoichiometric air/fuel ratio.

Such an in-cylinder injection engine is operated while individualoperation modes such as the above-mentioned compression stroke injectionmode (compressed lean mode or later lean mode), intake stroke injectionstoichiometric mode (stoichiometric mode), intake stroke injection leanmode (intake lean mode or earlier leanmode), intake stroke injectionenriched mode (enriched mode), and the like are appropriately selected.These operation modes are considered to be selected according to enginerotational speed and engine load.

Namely, the compressed lean mode is selected in a region where bothengine rotational speed and engine load are low; whereas, as the enginerotational speed or engine load increases therefrom, the intake leanmode, stoichiometric mode, and enriched mode are successively selectedin response to the magnitude of increase.

Since the amount of stepping on the accelerator pedal substantiallycorresponds to the engine load; when the compressed lean mode isselected, the accelerator pedal stepping amount is small, whereby theopening degree of the throttle valve is small. In the compressed leanmode where operation is effected in an ultra lean state with a very highair/fuel ratio, by contrast, unless a sufficient amount of intake air isprovided, the stratified flow is weakened, thereby making it difficultto effect stable burning. Accordingly, when the throttle valve openingis small and the intake air amount is restricted, it becomes difficultto effect operation in the compressed lean mode.

Therefore, in the in-cylinder injection engine, as mentioned above, abypass passage (air bypass passage) bypassing the throttle valve isformed, and the intake amount correction is performed so as tocompensate for the air amount restricted by the throttle valve, whilecontrolling a valve (air bypass valve) attached to the air bypasspassage.

Meanwhile, in such an in-cylinder injection engine, among the operationmodes, the air/fuel ratio to be controlled varies, and the fuelinjection stroke changes, whereby the amount of intake required forobtaining the same torque differs among the operation modes, and theintake vacuum for obtaining the same torque differs among the operationmodes as well.

Since the intake vacuum for obtaining the same torque differs among theoperation modes, when the relationship between the engine operationstate and the intake correction amount or valve opening degree isuniformly set as mentioned above, for example, an optimal intakecorrection amount cannot be set for each operation mode, therebydeteriorating drivability.

In view of the problems mentioned above, it is an object of the presentinvention to provide a control unit for an in-cylinder injectioncombustion engine, which can set an appropriate intake correction amountfor each operation mode in the in-cylinder injection internal combustionengine in order to improve the drivability in the in-cylinder injectioninternal combustion engine.

DISCLOSURE OF THE INVENTION

To this end, the present invention provides a control unit for anin-cylinder injection internal combustion engine in which fuel isdirectly injected into a combustion chamber and is adapted to select,according to an operation state of the internal combustion engine, acompression stroke injection mode for mainly injecting fuel at acompression stroke and an intake stroke injection mode for mainlyinjecting fuel at an intake stroke; the control unit comprisingoperation state detecting means for detecting an operation state oroperation environmental state of the internal combustion engine, intakeamount correcting means for changing an amount of intake supplied to theinternal combustion engine, intake correction amount setting means forsetting, according to a predetermined relationship, the intakecorrection amount according to the operation state detected by theoperation state detecting means, and intake amount correction controlmeans for controlling operation of the intake amount correcting meansaccording to the intake correction amount set by the intake correctionamount setting means, wherein the relationship between the operationstate and the intake correction amount is set differently between thecompression stroke injection mode and the intake stroke injection mode.

Owing to this configuration, the intake amount can be appropriatelycorrected for each of the operation modes such as compression strokeinjection mode and intake stroke injection mode in the in-cylinderinjection internal combustion engine, thus allowing drivability toimprove in the in-cylinder injection internal combustion engine.

Preferably, the intake amount correction control means is configured soas to correct, upon an idling operation of the internal combustionengine, the intake amount according to the above-mentioned relationshipbetween the operation state and the intake correction amount, while therelationship between the operation state and the intake correctionamount used upon the idling operation is set differently between thecompression stroke injection mode and the intake stroke injection mode.

Consequently, in particular, the intake amount can be appropriatelycorrected upon the idling operation where intake amount correctionbecomes important, thus allowing the drivability in the in-cylinderinjection internal combustion engine to efficiently improve.

It is preferable that the intake amount in the compression strokeinjection mode when the internal combustion engine is idling be setgreater than the intake amount in the intake stroke injection mode whenthe internal combustion engine is idling.

Preferably, the internal combustion engine further comprises targetair/fuel ratio setting means for setting a target air/fuel ratioaccording to a result of detection of the operation state detectingmeans, and the target air/fuel ratio set in the compression strokeinjection mode is leaner than the target air/fuel ratio set in theintake stroke injection mode.

Specifically, as the operation state detecting means, the one detectinga rotational speed of the internal combustion engine, the one detectingan accelerator operation state, the one detecting an opening degree ofan intake throttle valve, the one detecting a shift state of atransmission coupled to the internal combustion engine, the onedetecting an atmospheric pressure, the one detecting operaation state ofan accessory directly or indirectly driven by the internal combustionengine, or the one detecting a substantially full close state of theintake throttle valve can be used.

Preferably, the intake correction means corrects a bypass air amount ofthe intake throttle valve.

Preferably, the internal combustion engine comprises anelectrically-driven intake throttle valve, and the intake amountcorrecting means corrects an opening degree of the intake throttlevalve.

Preferably, the operation state is a state of load applied to theinternal combustion engine, and the intake correction amount is set incorrelation with an intake opening area which is adjusted in accordancewith the state of load.

In this case, it is preferred that an amount of change in the intakecorrection amount with respect to a change in the intake opening area beset greater in the compression stroke injection mode than in the intakestroke injection mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a main part of acontrol unit for in-cylinder injection internal combustion engine as anembodiment of the present invention;

FIG. 2 is a view for explaining an intake correction amount settingcharacteristic in the control unit for in-cylinder injection internalcombustion engine as an embodiment of the present invention;

FIG. 3 is a view for explaining an intake correction amount settingcharacteristic in the control unit for in-cylinder injection internalcombustion engine as an embodiment of the present invention;

FIG. 4 is a view showing a configuration of a main part of anin-cylinder injection internal combustion engine in accordance with anembodiment of the present invention;

FIG. 5 is a control block diagram showing the in-cylinder injectioninternal combustion engine in accordance with an embodiment of thepresent invention; and

FIG. 6 is a view for explaining operation modes of the in-cylinderinjection internal combustion engine in accordance with an embodiment ofthe present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to the drawings, a description will hereinafter be madeabout modes for carrying out the present invention. Namely, theexplanation will be made with reference to FIGS. 1 to 6 which illustratea control unit for in-cylinder injection internal combustion engine asan embodiment of the present invention.

First, the configuration of the in-cylinder injection internalcombustion engine (hereinafter referred to as in-cylinder injectionengine) will be explained with reference to FIG. 4.

Depicted in FIG. 4 are an engine main body 1, an intake passage 2, athrottle-valve-installed section 3, an air cleaner 4, a bypass passage(second bypass passage) 5, and a second air bypass valve (#2ABV) 6 whichcan adjust the air amount flowing through the bypass passage 5 andfunction as intake amount correcting means. The intake passage 2comprises, successively connected from the upstream side, an intake pipe7, a surge tank 8, and an intake manifold 9. The bypass passage 5 isdisposed upstream the surge tank 8. While the bypass valve 6 is drivenby a stepping motor so as to attain a predetermined opening degree, itsopening degree may be adjusted by a duty control of a solenoid valve.

Further, means 12 is equipped with an idle speed control function andcomprises a bypass passage (first bypass passage) 13 and a first airbypass valve (#1ABV) 14 as a bypass valve. The #1ABV 14 is driven by anon-depicted stepping motor and functions as intake amount correctingmeans.

Also provided is a throttle valve (intake throttle valve) 15. Though theone mechanically interlocked with an accelerator pedal (not depicted) isused here, an electric-motor-driven valve known as drive-by-wire (DBW)may also be used as the throttle valve 15. In this case, the bypassvalve may be omitted, so that the driving of the electric motor iscorrected by an extent corresponding to the correction air amountobtained by this bypass valve.

Here, the first bypass passage 13 and the second bypass passage 5 areconnected to the intake passage 2 respectively by their upstream anddownstream ends, while bypassing the portion of the intake passage 2 towhich the throttle valve 15 is attached.

Opening/closing control of each of the second air bypass valve 6 and thefirst air bypass valve 14 is performed via an electronic control unit(ECU) 16.

Also provided are an exhaust passage 17 and a combustion chamber 18.Opening portions of the intake passage 2 and the exhaust passage 17 withrespect to the combustion chamber 18, i.e., an intake port 2A and anexhaust port 17A, are respectively equipped with an intake valve 19 andan exhaust valve 20.

Numeral 21 refers to a fuel injection valve (injector), which isdisposed in this engine so as to directly inject fuel into thecombustion chamber 18.

Further provided are a fuel tank 22, fuel supply paths 23A to 23E, alow-pressure fuel pump 24, a high-pressure fuel pump 25, a low-pressureregulator 26, a high-pressure regulator 27, and a delivery pipe 28;whereby fuel within the fuel tank 22 is driven by the low-pressure fuelpump 24 and is further pressurized by the high-pressure fuel pump 25 soas to be supplied, in a predetermined high-pressure state, to theinjector 21 through the fuel supply paths 23A and 23B and the deliverypipe 28. Here, the fuel pressure emitted from the low-pressure fuel pump24 is adjusted by the low-pressure regulator 26, whereas the fuelpressure pressurized by the high-pressure fuel pump 25 so as to beguided to the delivery pipe 28 is adjusted by the high-pressureregulator 27.

Also provided are an exhaust gas recirculation passage (EGR passage) 29for recirculating the exhaust gas within the exhaust passage 17 of theengine 1 into the intake passage 2, a stepping motor type valve (EGRvalve) 30 as exhaust gas amount adjusting means for adjusting the amountof recirculation of exhaust gas flowing into the intake passage 2through the EGR passage 29, a flow path 31 for returning blow-by gas, apassage 32 for positive crankcase ventilation, a valve 33 for positivecrankcase ventilation, a canister 34, and an exhaust gas purifyingcatalyst 35 (catalytic converter rhodium here).

As shown in FIG. 4, the ECU 16 controls not only the air bypass valves 6and 14 but also the injector 21, an ignition coil for a non-depictedspark plug, and the EGR valve, and performs fuel pressure control bymeans of the high-pressure regulator 27. Accordingly, connected to theECU 16 are an airflow sensor 44, an intake temperature sensor 36, athrottle position sensor (TPS) 37 for detecting the throttle openingdegree, an idle switch 38, an air conditioner switch (not depicted), agear position sensor (not depicted), a vehicle speed sensor (notdepicted), a power steering switch (not depicted) for detecting anoperation state of a power steering, a starter switch (not depicted) , afirst cylinder sensor 40, a crank angle sensor 41, a water temperaturesensor 42 for detecting the temperature of cooling water for the engine,an O₂ sensor 43 for detecting the oxygen concentration in exhaust gas,and the like.

Here, the engine rotational speed can be computed according to the crankangle sensor 41. For example, such an engine rotational speed computingfunction is implemented within the ECU 16. While the crank angle sensor41 and this engine rotational speed computing function constitute anengine rotational speed sensor, the crank angle sensor 41 is alsoreferred to as engine rotational speed sensor here for convenience.

In the following, contents of control concerning the engine through theECU 16 will be explained with reference to the control block diagram ofFIG. 5.

This engine switches, according to its operation state, betweenpre-mixture burn operation which can be established by uniformlyinjecting fuel into the fuel combustion chamber 18 and a stratified burnoperation which can be established by concentrating the injected fuelaround the non-depicted spark plug facing into the combustion chamber18.

This engine is provided, as engine operation modes, with four fuelinjection modes comprising a later lean stratified burn operation mode(later lean mode) in which fuel is injected at a compression stroke soas to perform stratified lean burn, an earlier lean burn operation mode(earlier lean mode) in which fuel is injected at an intake stroke so asto perform pre-mixture burn, a stoichiometric feedback burn operationmode (stoichiometric mode), and an open-loop burn operation mode(stoichiometric mode or enriched mode), as well as a fuel cut mode forstopping (cutting) fuel injection.

By the control unit for this in-cylinder injection internal combustionengine, one of these modes is selected according to an engine operationstate, a vehicle driving state, or the like, thus controlling the fuelsupply. Here, in each fuel injection mode, cases where the EGR isactuated and not actuated are set.

Here, further explanation will be made about the fuel injection modes.Namely, in general, the enriched operation mode, stoichiometricoperation mode, earlier lean mode, and later lean mode are set withrespect to engine rotational speed Ne and engine load Pe so as to attaina tendency in terms of region such as that shown in FIG. 6.

Among the above-mentioned fuel injection modes, the later lean mode canrealize the leanest burn (where the air/fuel ratio is on the order of 30to 40). In this mode, fuel injection is performed at a stage very closeto an ignition timing such as the later stage of a compression stroke,and the fuel is concentrated in the vicinity of the spark plug so as tobe partially enriched, while attaining a lean state as a whole.Consequently, economical operation can be performed while ignitabilityand combustion stability are secured.

While the earlier lean mode can realize lean burn (where the air/fuelratio is on the order of 20 to 24) as well, fuel is injected in thismode at the intake stroke earlier than that performed in the later leanmode, so that fuel is diffused within the combustion chamber, thusmaking the overall air/fuel ratio lean. Consequently, a certain degreeof output is maintained while ignitability and combustion stability aresecured, whereby economical operation can be performed.

In the stoichiometric operation mode, a sufficient engine output canefficiently be obtained while the air/fuel ratio is kept at thestoichiometric state or in the vicinity thereof according to the outputof the O₂ sensor.

In the open-loop burn operation mode, burning is effected at thestoichiometric air/fuel ratio or an (enriched) air/fuel ratio richerthan that, by open-loop control in order to obtain sufficient outputupon acceleration, starting, or the like.

Such operation modes are selected by a functional section (modeselecting section) 102 disposed within the ECU 16 as shown in FIG. 1with a regional tendency such as that shown in FIG. 6 according toinformation (engine rotational speed Ne and engine load Pe) from anoperation state detecting means 101. Then, according to each mode, anair/fuel ratio is set according to the engine operation state, and afuel injection valve control amount such as fuel injection amount orfuel injection timing is set by a fuel injection valve control means 105so as to control the fuel injection valve 21, while an intake amount(intake correction amount) is controlled through the ABV valves 6 and 14according to thus set air/fuel ratio.

Here, an explanation will be made about the opening degree control ofeach of the valves 6 and 14 (i.e., intake amount correcting means),which is a characteristic feature of the present invention. Namely, asshown in FIG. 1, in the ECU 16, a function (intake correction amountsetting means) 110 for setting a required air amount (referred to asintake correction amount since it corrects the intake effected by thethrottle valve) according to the information (engine operation state)from the operation state detecting means 101, and a function (intakecorrection amount control means) 111 for outputting an instructionsignal to each of the valves 6 and 14 in response to the required airamount set by the intake correction amount setting means 110 control theopening degree of each of the valves (intake amount correcting means) 6and 14.

The intake correction amount setting means 110 sets the intakecorrection amount according to the information from the operation statedetecting means 101. Specifically, as shown in FIG. 1, it takes in notonly the engine rotational speed Ne and the engine load Pe determinedaccording to the data detected by the throttle position sensor 37 or anon-depicted accelerator position sensor or the like, but also states ofengine operation environments, i.e., data from a shift position sensor121 for detecting a shift state of the transmission, an atmosphericpressure sensor 122, an air conditioner switch 123 for detecting anactuation state of the air conditioner as an accessory, a power steeringswitch 124 for detecting an actuation state of the power steering as anaccessory, an idle switch 38, and the like; and sets the intakecorrection amount from a map [predetermined relationship (betweenoperation state and intake correction amount)] according to these data.

Namely, as shown in FIG. 5, a target engine load Pe (target Pe) isinitially set, according to a map, from a throttle opening degree θthdetected by the throttle sensor or the engine rotational speed Ne basedon the output of the non-depicted accelerator opening sensor and theinformation detected by the crank angle sensor (block B1) On the otherhand, based on the information from the air conditioner switch, when theair conditioner is on, an air-conditioner-related correction amountΔPeac is set from the engine rotational speed Ne according to a map(block B2). Based on the information from the power steering switch,when the power steering is on, a power-steering-related correctionamount ΔPeps is set from the engine rotational speed Ne according to amap (block B3). Based on the information from the inhibitor switch, uponstarting, an inhibitor-related correction amount ΔPeinh is set from theengine rotational speed Ne according to a map (block B4).

Also, though not depicted, for the shift position sensor 121 and theatmospheric pressure sensor 122, correction amounts corresponding totheir respective parameters are set.

Then, according to these specific correction amounts ΔPeac, ΔPeps,ΔPeinh, and the like, the target Pe is appropriately corrected. Thuscorrected target Pe is appropriately filtered through a switch S1 (blockB5), and a control amount Pos concerning a valve opening degreecorresponding to a required air amount (or target intake air amount) Qis set, according to a map, from thus obtained target Pe and the enginerotational speed Ne.

As shown in block B7, in order to set the control amount Pos, from aplurality of maps, the one corresponding to the engine operation stateis selectively used, and a signal is outputted through switches S2 andS3 in response to the engine operation state. Here, maps are providedfor three modes, as the engine operation states, comprising the laterlean mode that yields the leanest burn, the earlier lean mode thatyields the next leanest burn thereto, and an EGR-actuated state in thestoichiometric operation mode; and the required air amount is set onlyin these modes.

In the case where the idle operation state is established, by a switchS4, a control amount #1ABVPos (which becomes a target opening degreebased on the #1ABV valve in this case) for a required air amount (ortarget intake air amount) #1ABVQ based on feedback of the enginerotational speed is set as shown in block B8.

The functional section for setting the amount corresponding to therequired air amount Q, #1ABVQ, through the above-mentioned blocks B7 andB8 is equivalent to the required air amount setting means (intakecorrection amount setting means) 110.

In response to thus obtained control amount Pos or #1ABVPos, setting ofthe opening position of the air bypass valve 6 or duty cycle (block B10)and setting of the air bypass valve 14 (block B11) are effected, wherebythe air bypass valves 6 and 14 are controlled so as to attainpredetermined states.

Meanwhile, in the compression stroke injection mode (later lean) in thein-cylinder injection engine, since ultra-lean burning is effected, theair/fuel ratio is set very high, whereby the intake air amount is quitelarge in relation to the engine-generated torque. Consequently, theintake amount is corrected in a region where the magnitude of intakevacuum is relatively low. In the intake stroke injection mode, bycontrast, since operation is performed under the earlier lean mode orstoichiometric mode with a relatively high air/fuel ratio, the intakeair amount is not relatively large in relation to the engine-generatedtorque, whereby the intake amount is corrected in a region where themagnitude of intake vacuum is relatively large.

For example, the solid line shown in FIG. 2 indicates intake air amountQ in relation to intake opening area S. As depicted, the intake airamount control (intake correction amount control) in the compressionstroke injection mode (later lean) is performed in a region where theintake opening area S is relatively large, whereas the intake air amountcontrol (intake correction amount control) in the intake strokeinjection mode is performed in a region where the intake opening area Sis relatively small. Here, the intake opening area S corresponds to theengine load state and is determined according to the opening degrees ofthe throttle valve (intake throttle valve) 15 and the ABVs (intakeamount correcting means) 6 and 14.

In FIG. 2, point X1 indicates a point where the intake opening area Sand the intake air amount Q correspond to each other when engine torqueTA is generated in the intake stroke injection mode, whereas point X2indicates a point where the intake opening area S and the intake airamount Q correspond to each other when engine torque TA substantiallythe same as that at point X1 is generated in the compression strokeinjection mode.

As depicted, when the intake opening area S is increased by apredetermined amount S1 at the point X1 in the intake stroke injectionmode, the intake correction amount increases by Q1. By contrast, whenthe intake opening area S is increased by the predetermined amount S1 atthe point X2 in the compression stroke injection mode as in the case ofthe point X1, the intake correction amount increases by Q2. This intakecorrection amount Q2 is smaller than the intake correction amount Q1 inthe case of the point X1.

The intake amount control in the intake stroke injection mode iseffected in a region where the intake opening area S is relativelysmall. Since this region is an area where the magnitude of intake vacuumdownstream the throttle valve 15 is relatively large, the intake openingarea S and the intake air amount Q increase substantially linearly. Bycontrast, the intake amount control in the compression stroke injectionmode is effected in a region where the intake opening area S isrelatively large. Since this region is an area where the magnitude ofintake vacuum downstream the throttle valve 15 is relatively small, theintake opening area S and the intake air amount Q deviate from theirlinear relationship of increase, whereby the intake air amount Q doesnot increase so much as the intake opening area S increases. Here, thedotted line in FIG. 2 indicates a case where the intake opening area Sand the intake air amount Q maintain a linear relationship therebetween.

Here, in the case where the intake opening area S and the control amountPos concerning the valve opening degree are substantially in proportionto each other, in order to increase the intake opening area S by apredetermined amount S1, it is sufficient for the control amount Pos tobe increased by a correction control amount P1. In the case where theintake opening area S and the control amount Pos concerning the valveopening degree are not in proportion to each other, an approximateexpression of their relationship or the like may be used to compute acorrection control amount P2 from the intake opening area S, and thecontrol amount Pos may be increased by thus computed correction controlamount P2.

Thus, since the intake air amount changing in relation to the intakeopening area varies; when the same map (relationship between the engineoperation state and the control amount Pos) is used for the controlamount concerning the valve opening degree for adjusting the intakeopening area in both intake stroke injection mode and compression strokeinjection mode, an optimal intake correction amount may not be set foreach operation mode, thus deteriorating drivability.

Therefore, in this apparatus, different maps (relationships between theengine operation state and control amount Pos) are respectively set forthe intake stroke injection mode and the compression stroke injectionmode, so that the intake correction control is performed according tothe map for each mode.

Here, different maps (relationships) may be set respectively for theintake stroke injection mode and the compression stroke injection modeconcerning not only the relationship between the engine operation state(engine rotational speed Ne and engine load information Pe inparticular) and the control amount Pos, but also correction amountsbased on other data, i.e., those from the shift position sensor 121,atmospheric pressure sensor 122, air conditioner switch 123, powersteering switch 124, idle switch 38, and the like, so as to perform theintake correction control.

For example, FIG. 3 shows a state of control for the idle speed Neeffected when the air conditioner switch 123 is turned on from its offstate. Here, the corresponding intake amount is adjusted from Q1 to Q3in the case of the earlier lean (intake stroke injection), whereby theidle speed Ne is controlled so as to increase from Ni1 to Ni2. In thelater lean (compression stroke injection), on the other hand, the intakeamount is adjusted from Q2 to Q4, whereby the idle speed Ne iscontrolled so as to increase from Nil to Ni2.

As depicted, between the intake stroke injection mode and thecompression stroke injection mode, not only the basic intake amountvaries but also the intake correction amount differs, i.e., becomes αand β respectively in the intake stroke injection mode and thecompression stroke injection mode. Accordingly, for the intakecorrection amount control based on the air conditioner switchinformation, it is preferred that different maps (relationships) be setrespectively for the intake stroke injection mode and the compressionstroke injection mode.

As a method other than that mentioned above, a common intake correctionamount may be set among the individual operation modes, and amode-related coefficient (gain) may be set for each mode, so that thusset intake correction amount is adjusted in terms of gain by itsmode-related coefficient, thus setting a final intake correction amount(used for control).

In the following, with reference to FIG. 5, respective controls for theinjector, ignition coil, and EGR will be explained.

In order to drive the injector, it is necessary to set the injectionstarting timing and injection terminating timing of the injector. Here,an injector driving time Tinj and the injection terminating timing ofthe injector are set, and based thereon, as the injection startingtiming of the injector is counted backward, the injector driving timingis determined. These settings are effected by the ECU 16 according tothe engine operation state.

In order to set the injector driving time Tinj, an air/fuel ratio isinitially set (block B12), according to a map, from the corrected targetPe after filtering (block B6) and the engine rotational speed Ne. Also,in this case, different setting maps are provided for four modescomprising the EGR-actuated state in the later lean mode, EGR-stoppedstate in the later lean mode, earlier lean mode, and open-loop mode; andthe one corresponding to the engine operation mode is selectively used.

From thus obtained air/fuel ratio A/F and an intake amount Qpb detectedby the air flow sensor, the injector driving time Tinj is computed(block B13).

This injector driving time Tinj is corrected in terms of unequalinjector ratios among cylinders (block B14) and dead times amongcylinders (block B15). On the other hand, a deceleration injection timeTDEC is computed from the target Pe and the engine rotational speed Ne(block B16). When the operation is in both decelerated state and laterlean, of the injector driving time Tinj obtained at the block B13 andthe deceleration injection time TDEC, the smaller value is selectedthrough a switch S5 (block B17) and is determined as the injectordriving time.

Also, since the air/fuel ratio A/F changes as the above-mentioned intakeair amount is corrected, the injector driving time is corrected as theintake air amount is corrected, so as to attain a constant air/fuelratio A/F, thereby preventing exhaust gas performances fromdeteriorating.

Also, the injection terminating timing of the injector is set (blockB18), according to a map, from the corrected target Pe after filtering(block B6) and the engine rotational speed Ne. In this case, differentsetting maps are provided for four modes comprising the EGR-actuatedstate in the later lean mode, EGR-stopped state in the later lean mode,earlier lean mode, and open-loop or stoichiometric feedback operationmode; and the one corresponding to the engine operation mode isselectively used.

In the case of later lean mode, thus obtained injection terminatingtiming is corrected in terms of water temperature so as to yield aninjection terminating timing.

Based on thus obtained injector driving time Tinj and injectionterminating timing, the injector is driven.

Also, the ignition timing of the spark plug effected by the ignitioncoil is set (block B20), according to a map, from the corrected targetPe after filtering (block B6) and the engine rotational speed Ne. Inthis case, different setting maps are provided for five modes comprisingthe EGR-actuated state in the later lean mode, EGR-stopped state in thelater lean mode, earlier lean mode, EGR-actuated state in stoichiometricfeedback operation, and EGR-stopped state in open-loop or stoichiometricfeedback operation. Thus obtained ignition timing is subjected tovarious kinds of retard corrections (block B 21), and the ignition coilis controlled on the basis thereof.

Also, the flow rate of the EGR is set (block B22), according to a map,from the corrected target Pe after filtering (block B6) and the enginerotational speed Ne. In this case, the setting maps are provided forfour modes comprising the later lean mode in the D range, later leanmode in the N range, stoichiometric feedback operation mode in the Drange, and stoichiometric feedback operation mode in the N range.

Thus obtained flow rate of the EGR is corrected in terms of watertemperature (block B23), and a control amount (duty cycle) correspondingto the opening degree is set (block B24), so as to control the flow rateof the EGR. Here, for the water temperature correction (block B23), mapscorresponding to engine operation states (two modes comprising the laterlean mode and stoichiometric feedback operation mode here) are used.

The control unit for in-cylinder injection internal combustion engine asan embodiment of the present invention sets different maps(relationships between engine operation state and control amount Pos)respectively for the intake stroke injection mode and compression strokeinjection mode, and the intake correction amount is controlled on thebasis thereof, whereby the intake correction amount can be optimallycorrected in each operation mode, thus improving drivability in eachoperation mode.

Also, as different maps (relationships) are set respectively for theintake stroke injection mode and the compression stroke injection modeconcerning not only the relationship between the engine operation state(engine rotational speed Ne and engine load information Pe inparticular) and the control amount Pos, but also correction amountsbased on other data, i.e., those from the shift position sensor 121,atmospheric pressure sensor 122, air conditioner switch 123, powersteering switch 124, idle switch 38, and the like, so as to perform theintake correction control; the intake correction amount can be optimallycorrected in each operation mode, thus improving drivability in eachoperation mode as well.

Such a technique for setting different maps (relationships) respectivelyfor the intake stroke injection mode and compression stroke injectionmode is quite effectively employed upon idling operation of an enginehaving a high intake-controlling effect in particular.

Though the above-mentioned embodiment explains a case where the intakeair amount is corrected by use of bypass valves, similar effects canalso be obtained when such a technique is applied to anelectric-motor-driven throttle valve which is driven by an electricmotor such as that mentioned above.

Capability of Exploitation in Industry

An appropriate intake amount correction can be effected for eachoperation mode such as compression stroke injection mode and intakestroke injection mode in an in-cylinder injection internal combustionengine, thus allowing drivability to improve in the in-cylinderinjection internal combustion engine. Consequently, the presentinvention is suitable for an engine for a vehicle such as automobile. Itcan simultaneously satisfy various requirements for a vehicle enginesuch as improvement in drivability due to stable burning, reduction ofoperation cost due to lower fuel consumption, environmental protectiondue to acceleration of exhaust gas purification, and the like, thusbeing quite useful.

I claim:
 1. A control unit for an in-cylinder injection internalcombustion engine in which fuel is directly injected into a combustionchamber and is adapted to select, according to an operation state ofsaid internal combustion engine, a compression stroke injection mode formainly injecting fuel at a compression stroke and an intake strokeinjection mode for mainly injecting fuel at an intake stroke;saidcontrol unit comprising:load correlation value detecting means (37) fordetecting a load correlation value of said internal combustion engine,rotational speed detecting means (41) for detecting an engine rotationalspeed of said internal combustion engine, target load level settingmeans (B1) for setting a target load level according to the loadcorrelation value detected by said load correlation value detectingmeans (37) and the engine rotational speed detected by said rotationalspeed detecting means (41), target air/fuel ratio setting means (B12)for setting a target air/fuel ratio at a first air/fuel ratio which ison a fuel-leaner side of a stoichiometric air/fuel ratio when saidcompression stroke injection mode is selected, and at a second air/fuelratio which is on a fuel-richer side of said first air/fuel ratio whensaid intake stroke injection mode is selected, intake amount correctingmeans (6) for changing an amount of intake supplied to said internalcombustion engine, intake correction amount setting means (110) forsetting, according to the target load level set by said target loadlevel setting means (B1), a first intake correction amount required insaid compression stroke injection mode or a second intake correctionamount required in said intake stroke injection mode, and intake amountcorrection control means (111) for controlling operation of said intakeamount correcting means (6) according to said first or second intakecorrection amount set by said intake correction amount setting means(110).
 2. The control unit for an in-cylinder injection internalcombustion engine of claim 1, wherein said intake amount correctioncontrol means (110) sets said first intake correction amount requiredfor said first air/fuel ratio in said compression stroke injection modegreater than said second intake correction amount required for saidsecond air/fuel ratio in said intake stroke injection mode.
 3. Thecontrol unit for an in-cylinder injection internal combustion engine ofclaim 1, wherein said intake amount correction control means (111) setsa control amount of said intake amount correcting means (6) required ineach of said injection modes according to a parameter which is incorrelation with an intake opening area adjusted in accordance with astate of load of said internal combustion engine.
 4. The control unitfor an in-cylinder injection internal combustion engine of claim 3,wherein said intake amount correction control means (111) sets a firstcontrol amount of said intake amount correcting means (6) for obtaininga predetermined air amount required in said compression stroke injectionmode greater than a second control amount of said intake amountcorrecting means (6) for obtaining said predetermined air amountrequired in said intake stroke injection mode.
 5. The control unit foran in-cylinder injection internal combustion engine of claim 1,comprising operation environmental state detecting means (122, 123, 124)for detecting at least one of a shift state of a transmission coupled tosaid internal combustion engine, operation state of an accessorydirectly or indirectly driven by said internal combustion engine, and anatmospheric pressure.
 6. The control unit for an in-cylinder injectioninternal combustion engine of claim 5, comprising target load levelcorrecting means which determines a target environmental load levelaccording to an operation environmental state detected by said operationenvironmental state detecting means (122, 123, 124), and determines acorrected target load level from said target environmental load leveland the target load level set by said target load level settingmeans;wherein said intake correction amount setting means (110) sets,according to the corrected target load level determined by said targetload level correcting means, said first or second intake correctionamount required in said compression stroke injection mode or intakestroke injection mode.
 7. The control unit for an in-cylinder injectioninternal combustion engine of claim 6, wherein said target load levelcorrecting means computes an environmental load correction amountcorresponding to each operation environmental state detected by saidoperation environmental state detecting means (122, 123, 124) and theengine rotational speed detected by said rotational speed detectingmeans (41).
 8. The control unit for an in-cylinder injection internalcombustion engine of claim 5, wherein said load correlation valuedetecting means is constituted by throttle valve opening detecting means(37) for detecting an opening degree of a first throttle valve disposedin an intake passage of said internal combustion engine.
 9. The controlunit for an in-cylinder injection internal combustion engine of claim 8,wherein said intake correction amount setting means (110) sets, whensaid throttle valve opening detecting means (37) detects a full openstate of said throttle valve, a first intake correction amountcorresponding to a predetermined change in an operation environmentalstate detected by said operation environmental state detecting means(122, 123, 124) in said compression stroke injection mode greater than asecond intake correction amount corresponding to said predeterminedchange in the operation environmental state in said intake strokeinjection mode.
 10. The control unit for an in-cylinder injectioninternal combustion engine of claim 5, comprising environmental intakeamount correcting means which determines an environmental correctionintake amount according to an operation environmental state detected bysaid operation environmental state detecting means (122, 123, 124),determines a third intake correction amount from said environmentalcorrection intake amount and said first intake correction amountrequired in said compression stroke injection mode and set by saidintake correction amount setting means (110), and determines a fourthintake correction amount from said environmental correction intakeamount and said second intake correction amount required in said intakestroke injection mode and set by said intake correction amount settingmeans (110).
 11. The control unit for an in-cylinder injection internalcombustion engine of claim 10, wherein said environmental intake amountcorrecting means computes an environmental correction intake amountcorresponding to each operation environmental state detected by saidoperation environmental state detecting means (122, 123, 124) and theengine rotational speed detected by said rotational speed detectingmeans (41).
 12. The control unit for an in-cylinder injection internalcombustion engine of claim 10, wherein said intake correction amountsetting means (110) sets said first intake correction amount requiredfor said first air/fuel ratio in said compression stroke injection modegreater than the second intake correction amount required for saidsecond air/fuel ratio in said intake stroke injection mode.
 13. Thecontrol unit for an in-cylinder injection internal combustion engine ofclaim 10, wherein said intake amount correction control means (111) setsa first control amount of said intake amount correcting means (6) forobtaining a predetermined air amount required in said compression strokeinjection mode greater than a second control amount of said intakeamount correcting means (6) for obtaining said predetermined air amountrequired in said intake stroke injection mode.
 14. The control unit foran in-cylinder injection internal combustion engine of claim 1,including an air bypass passage (5) which bypasses a first throttlevalve (15) disposed in an intake passage of said internal combustionengine and communicates with said intake passage upstream and downstreamsaid first throttle valve (15), and an electric air bypass valve (6) foropening and closing the air bypass passage (5);wherein said intakeamount correction control means (111) controls said air bypass valve (6)such that an intake amount supplied through said air bypass passage (5)becomes said first or second intake correction amount.
 15. The controlunit for an in-cylinder injection internal combustion engine of claim14, wherein said intake amount correction control means (111) sets afirst opening control amount of said air bypass valve (6) for obtaininga predetermined air amount required in said compression stroke injectionmode greater than a second operation opening control amount of said airbypass valve (6) for obtaining said predetermined air amount required insaid intake stroke injection mode.
 16. The control unit for anin-cylinder injection internal combustion engine of claim 1, whereinsaid load correlation value detecting means is constituted byaccelerator opening detecting means (37) for detecting an opening degreeof an accelerator pedal which is attached to a vehicle installing saidinternal combustion engine therein and is operated by a driver;whereinsaid internal combustion engine comprises:a second throttle valve (6)for electrically opening and closing an intake passage of said internalcombustion engine, target opening degree setting means for setting atarget opening degree of said second throttle valve (6) according to anopening degree of the accelerator pedal detected by said acceleratoropening detecting means (37), and throttle opening control means forcontrolling said second throttle valve (6) so as to attain the targetopening degree set by said target opening degree setting means; whereinsaid intake amount correcting means is constituted by said secondthrottle valve (6) and throttle opening control means.
 17. The controlunit for an in-cylinder injection internal combustion engine of claim16, wherein said intake amount correction control means (111) sets afirst opening degree correction amount of said second throttle valvewith respect to said target opening degree for obtaining a predeterminedair amount required in said compression stroke injection mode greaterthan a second opening degree correction amount of said second throttlevalve with respect to said target opening degree for obtaining saidpredetermined air amount required in said intake stroke injection mode.18. The control unit for an in-cylinder injection internal combustionengine of claim 1, comprising intake amount detecting means (44) fordetecting an amount of intake supplied to said internal combustionengine,wherein said target air/fuel ratio setting means (B12) determinesthe target air/fuel ratio according to the intake amount detected bysaid intake amount detecting means (44) when said intake strokeinjection mode is selected, and according to the load correlation valuedetected by said load correlation value detecting means (37) when saidcompression stroke injection mode is selected.
 19. A control unit for anin-cylinder injection internal combustion engine in which fuel isdirectly injected into a combustion chamber and is adapted to select,according to an operation state of said internal combustion engine, acompression stroke injection mode for mainly injecting fuel at acompression stroke and an intake stroke injection mode for mainlyinjecting fuel at an intake stroke;said control unit comprising:loadcorrelation value detecting means (37) for detecting a load correlationvalue of said internal combustion engine, rotational speed detectingmeans (41) for detecting an engine rotational speed of said internalcombustion engine, target load level setting means (B1) for setting atarget load level according to the load correlation value detected bysaid load correlation value detecting means (37) and the enginerotational speed detected by said rotational speed detecting means (41),target air/fuel ratio setting means (B12) for setting a target air/fuelratio at a first air/fuel ratio which is on a fuel-leaner side of astoichiometric air/fuel ratio when said compression stroke injectionmode is selected, and at a second air/fuel ratio which is on afuel-richer side of said first air/fuel ratio when said intake strokeinjection mode is selected, intake amount correcting means (6) forchanging an amount of intake supplied to said internal combustionengine, intake correction amount setting means (110) for setting,according to the target load level set by said target load level settingmeans (B1), an intake correction amount, intake correction amountadjusting means (110) for adjusting said intake correction amountaccording to a correction coefficient corresponding to a selectedinjection mode, and intake amount correction control means (111) forcontrolling operation of said intake amount correcting means (6)according to the intake correction amount adjusted by said intakecorrection amount adjusting means (110) corresponding to each injectionmode.